The invention relates to an apparatus for regulating the temperature of a room or interior space. A known apparatus for controlling the heating of the interior space of a motor vehicle provides an interior room temperature sensor and an outside temperature sensor, connected in series, as well as a set point or reference source. The flow of heating medium through a heat exchanger is controlled on the basis of the sum of the signals from these sensors. However, a precise comparison with a preset set point value is not possible by these means. The known apparatus offers substantial relative advantages, but it also entails the disadvantage that the influence of the heating air temperature sensor on the heat exchanger is greater during a high heat output than during a low heat output, due to the additive combination of the controlled variables. The reverse is true of the influence of the interior space temperature sensor on the sum of the controlled variables. Correspondingly, for a constant preset set point, a relatively lower actual space temperature is obtained when the heat exchanger must be operated at a high heat output.